1. Field of the Invention
The present invention relates to a process for producing 2-amino or selected 2-(substituted)amino-5-mercapto-1,3,4-thiadiazoles.
2. Description of the Prior Art
2-Amino and many 2-(substituted)amino-5-mercapto-1,3,4-thiadiazoles have been found to be useful and important chemical intermediates in the synthesis of corrosion inhibitors, drugs, photographic chemicals and pesticides. For example, 2-(lower alkyl)amino-5-mercapto-1,3,4-thiadiazole compounds have been found useful as intermediates for herbicides. See U.S. Pat. No. 4,066,436 which issued to Kirkpatrick on Jan. 3, 1978.
In the past, there have been two reaction routes for producing these 1,3,4-thiadiazole compounds. One reaction route involves the reaction of thiosemicarbazide with carbon disulfide. See French Pat. No. 1,064,234, which issued to Horclois et al on May 12, 1954. This route is illustrated by the following equation (A) where 2-methylamine-5-mercapto-1,3,4-thiadiazole is prepared: ##STR1## However, the carbon disulfide reactant is a particularly flammable material and requires specific facilities for its handling. Additionally, this method requires the use of organic solvents during the reaction which increase the production cost of the desired product.
The second known route for making these compounds involves the reaction of hydrazine with thiocyanates. See U.S. Pat. No. 2,966,495, which issued to Song et al on Dec. 27, 1960. This reaction is illustrated by equation (B) shown below, where 2-amino-5-mercapto-1,3,4-thiadiazole compounds are produced: ##STR2##
While these corresponding thiocyanates are commercially available, they are relatively expensive and the production cost of 1,3,4-thiadiazole compounds will be necessarily high.